Lighting device for surface inspection

ABSTRACT

In a lighting device according to the present invention, light emitted from a light source (L 1 ) is introduced to a light guide input terminal of a fiber bundle ( 3 ) in which a plurality of optical fibers ( 2 ) are bundled and is used for illumination by being emitted from a light guide output terminal ( 2   b ); the light source (L 1 ) consists of a plurality of LEDs and the light from each LED is respectively introduced to one or more optical fibers ( 2 ).

TECHNICAL FIELD

The present invention relates to a lighting device for surfaceinspection used for the inspection of products etc in factories.

BACKGROUND ART

Lighting devices are employed for inspection of the external appearanceand/or defects of products etc in factories. For such lighting devices,lighting devices of higher luminous intensity than that of ordinarylighting devices are often required; for these purposes, halogen lampsare often employed as the light source. Illumination of the subject ofinspection is performed by directing the light emitted from a halogenlamp incorporated in the main device body of the lighting device ontoone end of an optical fiber bundle comprising a plurality of opticalfibers, and extracting this from the tip thereof.

However, although a halogen lamp has the advantage that high luminousintensity is obtained, the luminous intensity gradually decreases withtime of use, due to evaporation etc of the filament, with the resultthat it becomes unusable usually after about 2000 hours. Thus, since thelife of a halogen lamp is short, maintenance, involving replacement etc,must be carried out frequently and in addition, in cases whereinspection with the same luminous intensity is required, since theluminous intensity gradually decreases with period of use, operation tomaintain the same luminous intensity by constantly performing fineadjustment of the supplied voltage etc becomes necessary. Suchmaintenance or luminous intensity adjustment operations interfere withautomation of the product inspection step and constitute a factor thatadversely affects the inspection efficiency. Furthermore, owing to thecharacteristic of halogen lamps that their amount of light increases ordecreases only slowly in response to turning the power source on or off,in cases where, depending on the type of inspection, it is required thatthe light should be turned on and off instantaneously in stroboscopicfashion, the method must be adopted of cutting off the lightmechanically by means of a shutter or the like, leading to the drawbackthat the device becomes complicated and of large size. Also, since thehalogen lamp itself is comparatively large, there is the inconveniencethat making the main body of the device compact is difficult.

Although various devices have been considered in order to solve suchinconveniences, it has not been possible to solve any of the aboveproblems or solutions have been difficult to implement from the point ofview of cost, so the development of a lighting device for inspectionpurposes that does not have these problems is desired.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a lighting devicewhereby these problems are solved at a stroke and which basically adoptsa construction wherein LEDs are respectively mounted at the light guideinput terminals of optical fibers, and whereby an amount of lightsufficient for inspection purposes can be supplied in stable fashion,and which has a long life.

In order to achieve this object, a lighting device according to thepresent invention for surface inspection is constituted such that lightemitted from a light source is fed into the light guide input terminalof an optical fiber bundle obtained by bundling a plurality of opticalfibers and is employed for illumination by being extracted from thelight guide output terminal thereof, in which the light source comprisesa plurality of LEDs and the light that is emitted from each of the LEDsis arranged to be respectively guided into one or more optical fibers.

By means of such a construction, since a plurality of LEDs are employed,and the light that is emitted from each of the LEDs is respectivelyintroduced into each optical fiber (or two or more optical fibers), as awhole, luminous intensity that is fully sufficient for productinspection etc can be obtained by making the number of LEDs a largenumber. Furthermore, due to the characteristics of LEDs, compared with ahalogen lamp, an amount of light that is much more stable can bemaintained over a long period, making it possible to greatly reduce thework involved in maintenance and/or adjustment in order to maintain theluminous intensity level. Automation of the product inspection step cantherefore be facilitated, and the efficiency of inspection can beraised.

Also, in order to simplify the construction and to reduce as far aspossible the loss of light at the region of the junction of the opticalfibers and the LEDs, it is desirable that the light guide input terminalof the optical fibers is directly bonded to the light-emitting elementmain bodies of the LEDs.

Also, specifically, as a preferred embodiment aimed at increasing thecompactness and reducing the weight of the device, there may bementioned a device wherein a plurality of light-emitting element mainbodies that constitute the aforesaid LEDs are arranged so as to bedistributed on the surface of a circuit board. The plurality oflight-emitting element main bodies may be arranged distributed in matrixfashion on the surface of the printed circuit board.

When the light-emitting element main bodies are arranged distributed inthis way on the printed circuit board, the amount of heat that isgenerated by the closely packed LEDs becomes large and tends toaccumulate in the printed circuit board, so the amount of light emittedby the LEDs and their life may be reduced.

Accordingly, in order to efficiently remove this amount of heat, it isdesirable to arrange a cooling device in the vicinity of said circuitboard. Specifically, as such a cooling device, there may be provided aheat sink to the rear of the printed circuit board, or a Peltier elementfor cooling purposes may be adhered to the rear face of the circuitboard. Furthermore, it is desirable to provide a heat-removing fan forintroducing and circulating external atmosphere within the lightingdevice.

Also, in order to suppress generation of heat by the densely packedLEDs, it is desirable to provide a switch that turns on/off the suppliedpower of the light-emitting element main bodies. Specifically, a switchis desirable that is operated in pulse modulation mode. In this way,since the LEDs can be turned on/off in response to turning on/off of thesupplied power in an extremely short time of the order of microseconds,it becomes possible to achieve a considerable reduction in the amount ofheat generated by the densely packed LEDs, and, even in cases where,depending on the type of inspection, the light is required to be turnedon/off instantaneously in stroboscopic fashion, this can be achievedsimply by turning the power on/off, making it possible to meet suchdemands with an extremely simple construction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic overall view of a lighting device illustratingan embodiment of the present invention;

FIG. 2 is a partial cross-sectional view to a larger scale illustratingthe light source part in the embodiment of FIG. 1 to a larger scale;

FIG. 3 is a partial perspective view illustrating the light source partin the embodiment of FIG. 1 to a larger scale;

FIG. 4 is a partial perspective view illustrating the light source partin another embodiment to a larger scale;

FIG. 5 is a partial cross-sectional view to a larger scale illustratingthe light source part in yet a further embodiment to a larger scale;

FIG. 6 is a diagrammatic overall view illustrating an example of amodification of the lighting member in a lighting device according tothe present invention;

FIG. 7 is a diagrammatic overall view illustrating an example of anothermodification of a lighting device according to the present invention;and

FIG. 8 is a diagram illustrating an embodiment of a connector in alighting device according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is described below with referenceto FIG. 1 to FIG. 3.

Lighting device according to this embodiment is employed for productinspection in a factory. As shown in FIG. 1, it comprises a device mainbody 6 incorporating a light source L1, a lighting member 7 forilluminating the subject of inspection, and an optical fiber bundle 3connected between the device main body 6 and lighting member 7 fordirecting light emitted from light source L1 onto lighting member 7.

As shown in FIG. 2 and FIG. 3, light source L1 is constituted bymounting a plurality of light-emitting element main bodies 1 constitutedby LEDs in a vertical and horizontal matrix on the surface of a printedcircuit board 5. Preferably light-emitting element main bodies of thesurface light-emitting type are employed as light-emitting element mainbodies 1; in this embodiment, those which are employed for LEDs of theso-called high luminance or ultra-high luminance type are used. Thenumber of these is set at for example about 200, but the number will ofcourse vary depending on the degree of luminous intensity required.Power lines, not shown, are of course provided on printed circuit board5 for supplying power to the light-emitting element main bodies 1. Thesymbol 1 a shown in FIG. 2 is a lead that connects the power line withthe power source of each light-emitting element main body 1. At the backof the printed circuit board 5 there is stuck a heat sink 12 to removethe heat that is generated by the densely packed LEDs; a fan 13 ismounted for forcibly introducing and circulating external air in devicemain body 6. In addition, it is beneficial to increase the heat removaleffect by sticking a Peltier element (not shown) on to the back face ofprinted circuit board 5.

Apart from the above, in addition, although not shown, switches etc forturning on and off the power source device and/or this power supply areincorporated within this device main body 6. Also, in this embodiment,adjustment of the amount of light of the light-emitting element mainbodies 1 is performed by the so-called PWM Method (Pulse WidthModulation method), in which the power is employed in pulse form andadjustment is effected by altering the ratio of the on/off timesthereof.

One optical fiber 2 is respectively connected to each of the aforesaidlight-emitting element main bodies 1. Specifically, the end face 2 a ofoptical fiber 2 i.e. its optical input terminal 2 a is bonded to thelight-emitting face 1 b of light-emitting element main body 1 by meansof light-transmitting transparent adhesive resin 4. Also, each of theoptical fibers 2 that are respectively bonded to the light-emittingelement main bodies 1 are formed into a bundle within device main body 6and led out to the outside as an optical fiber bundle 3. Lighting member7 is connected at the tip portion thereof.

Optical fiber bundle 3 is constituted by a bundle of optical fibers 2covered with a tubular cover, the whole having flexibility and beingconstituted such that the lighting member 7 that is connected at the tipportion thereof can be moved into a position and attitude that can to acertain extent be freely chosen.

For the lighting member 7, a lighting member of well-known type isemployed. In this embodiment, as shown in FIG. 1, the lighting member isof cylindrical shape, and is arranged to expose the light guide outputends 2 b of a dense bundle of optical fibers 2 at its end face, so thatthe light that is emitted from light source L1 can perform illuminationby being led out from their light guide output ends 2 b through theoptical fiber bundle 3. Also, as shown in FIG. 6, lighting member 7could be of cylindrical shape, with the light guide output terminals 2 bbeing exposed in annular fashion at its end faces. With such anarrangement, a subject of inspection can be externally viewed andinspected through the through-hole 7 b of the lighting member 7, butshadows produced by illumination from the periphery of the subject ofinspection can be eliminated. Lighting members fitted with a lens orlighting members of various other types may be considered as thelighting member, but, since they are well known, description of these isomitted in the present Specification.

With a lighting device according to the present embodiment constructedas above, since a large number of LED light-emitting element main bodies1 are employed and each of the light-emitting element main bodies 1 arerespectively directly connected to the optical fibers 2, as a whole, afully sufficient luminous intensity for product inspection etc can beobtained, making it possible to reduce as far as possible loss of theamount of light in the region of the junction of the optical fibers 2and light-emitting element main bodies 1. Furthermore, since, comparedwith a halogen lamp, due to the characteristics of an LED, a much morestable amount of light can be maintained over a long period, operationsrelating to maintenance and/or adjustment to maintain the luminousintensity can be considerably reduced. Automation of the productinspection step is therefore facilitated, making it possible to improvethe efficiency of inspection. Also, since the LED light-emitting elementmain bodies 1 can be turned on or off in response to turning on or offof the power supply in an extremely short time of the order ofmicroseconds, the amount of heat generated by the closely packed LEDs isgreatly reduced, and even when instantaneous turning of the light on andoff in stroboscopic fashion is required, depending on the type ofinspection, this can be achieved simply by turning the power source onor off, making it possible to meet this requirement with an extremelystraightforward construction.

In particular, in the present embodiment, since a plurality oflight-emitting element main bodies 1 are arranged so as to bedistributed vertically and horizontally on printed circuit board 5,compactness and weight reduction of light source L1 can be achieved.

It should be noted that the present invention is not restricted to theembodiment described above. Various modifications are indicated below,in the description of which members corresponding to those of theforegoing embodiment are given the same reference symbols. For example,as shown in FIG. 4, optical fibers 2 may be mounted on ordinarycommercially available LEDs 1A wherein a power terminal 11 andtransparent cover 14 etc are mounted beforehand on light-emittingelement main body 1. In this case, as shown in this Figure, reduction inthe amount of loss of light in this junction region is achieved bymounting LED 1A on light guide input terminal 2 a of optical fiber 2 bymeans of a ball lens 8. Transparent adhesive resin 4 is employed tostick adjacent members together as in the embodiment described above.

Also, as shown in FIG. 5, two or more optical fibers 2 could be bondedto a single light-emitting element main body 1. Furthermore, variouscolors of the illuminating light could be set by employing incombination LEDs of different light emission color. In this way, it canbe arranged to apply illumination with the optimum color for inspection,without reducing the amount of light, thereby obtaining the benefit ofimproving the reliability of inspection etc.

Also, as shown in FIG. 7, a connector 9 for connection purposes could beprovided so as to enable a conventional optical fiber bundle 11 mountedon a lighting device of this kind to be used directly. If this is done,convenience in handling by the user can be improved. Reference symbol 10is a connector for purposes of connection with the device main bodymounted at the base of optical fiber bundle 11 in a prior art device. Ofcourse, such a connector for connection purposes can be directly mountedon the outside face of this device main body 6 so as to connect theoptical fiber bundle 11 employed in the conventional device.Furthermore, connection of the LEDs and optical fibers is not restrictedto the methods of the above embodiments and the lighting member can bereplaced by lighting members of various other types. Apart from this,the present invention is not restricted to the examples illustrated andcan be modified in various ways without departing from its essence.

For example, there may be mentioned an arrangement wherein, as shown inFIG. 8, an existing light guide 22 and a light guide output terminalaccording to the present invention are connected by providing aconnector 20 on device main body part 6. FIG. 8(a) is a perspective viewshowing the external appearance of this connector 20; FIG. 8(b) is adetail cross-sectional view showing the condition in which a light guide22 is fixed in connector 20. The plurality of optical fibers 2 that areled out from the aforementioned LEDs are fixed in a bundle by insertinginto a tip member 23, which is hollow, and the leading end face of thisoptical fiber bundle is polished to form a light guide output terminal.Also, this tip member 23 is fitted into a connection hole 20 a ofconnector 20, and is fixed in position in connector 20 by means of aball detent mechanism 24 constituted by fixing a ball 24 a to the tip ofspring 24 b. Specifically, tip member 23 is fixed in connector 20 byengagement of ball 24 a that is resiliently biased by means of spring 24b with an annular groove 23 a of tip member 23. The light guide inletterminal of a light-receiving member 22 a and the light guide outputterminal according to the present invention are connected by applyingpressure by engagement of a screw 21 with annular groove 22 b of thislight-receiving member 22 a with a light-receiving member 22 a of lightguide 22 fitted into connecting hole 20 a of this connector 20. Theshape of connector 20 is not restricted to that of this embodiment butcould be suitably selected so as to match the shape of thelight-receiving member of another existing light guide etc.

As described in detail above, the actions and benefits of the presentinvention are as follows.

Since a plurality of LEDs are employed and the light that is emittedfrom the LEDs is respectively introduced into the optical fibers (or twoor more optical fibers), as a whole, a luminous intensity that is fullysufficient for inspection of products etc can be obtained by making thenumber of LEDs a large number. This therefore makes it possible toemploy LEDs in a lighting device of this type in which conventionally ahalogen lamp was employed as light source for reasons of luminousintensity. Thus, as a result, various benefits are obtained byexploiting the characteristics of LEDs. Specifically, since, comparedwith a halogen lamp, due to the characteristics of an LED, a much morestable amount of light can be maintained over a long period, workrelating to maintenance and/or adjustment to maintain the luminousintensity can be considerably reduced. When used in product inspection,automation of this step is therefore facilitated, making it possible toimprove the efficiency of inspection.

In addition, since the light source is constituted of an assembly of aplurality of LEDs, various colors of the illuminating light could be setin a simple manner by employing in combination LEDs of different lightemission color, without reducing the luminous intensity as a whole.Consequently, the benefits of improving the reliability of inspectionetc can be obtained by adjusting so as to provide an optimumillumination color in accordance with the subject of inspection.

Also, if the light guide input end of the optical fiber is directlybonded to the LED light-emitting element main body, simplification ofthe construction can be achieved and loss of light at the region of thejunction of the optical fibers and LEDs can be reduced as far aspossible. If in this case a plurality of light-emitting element mainbodies are arranged so as to be distributed vertically and horizontallyon the printed circuit board, this contributes to automating assemblyand to improving the compactness of the light source.

Also, if a large number of light-emitting element main bodies aredensely arranged on the circuit board so as to obtain a sufficientluminous intensity that is necessary for product inspection and forincreasing the compactness of the light source etc, since the amount ofheat that is generated by the closely packed LEDs is removed byarranging a cooling device in the vicinity of the aforesaid substrate,accumulation of this amount of heat on the circuit board is prevented,and so reduction in the amount of light emitted by the LEDs is preventedand the life of the LEDs can be extended.

Furthermore, thanks to the provision of a switch that turns the suppliedpower of the light-emitting element main bodies on/off, the LEDs reactin an extremely short time, of the order of microseconds, to turning onor off of the supplied power and the amount of heat generated by thedensely packed LEDs is greatly reduced, so reduction of the amount oflight generated by the LEDs can be prevented and the life of the LEDsextended; also, even in cases where, depending on the type ofinspection, instantaneous turning of the light on and off instroboscopic fashion is required, this demand can be met simply byturning the power source on and off.

INDUSTRIAL APPLICABILITY

As described above, the present invention is particularly applicable inthe field of lighting devices for inspection that are used to illuminatea product etc for purposes of examining the external appearance of theproduct etc or for finding surface defects etc.

What is claimed is:
 1. A lighting device for surface inspection,comprising: a light source including a plurality of LEDs; and an opticalfiber bundle including a plurality of optical fibers, the optical fiberbundle having a light guide input terminal at one end of the bundle fromwhich light emitted from a light source is fed, and a light guide outputterminal at other end of the bundle from which light is extracted forillumination, wherein light emitted from each of the LEDs is guided intoone optical fiber, and the light guide input terminal of the opticalfibers is directly bonded to the LEDs, and wherein the LEDs are arrangedin matrix over the surface of the board.
 2. The lighting device forsurface inspection according to claim 1, wherein a cooling device isprovided in the vicinity of said board.
 3. The lighting device forsurface inspection according to claim 2, wherein, as said coolingdevice, a heat sink is provided in the rear of said board.
 4. Thelighting device for surface inspection according to claim 3, wherein aPeltier element for cooling purpose is adhered to the rear face of saidboard.
 5. The lighting device for surface inspection according to claim2, wherein, as said cooling device, a heat dissipating fan forintroducing and circulating external air to the lighting device isprovided.
 6. The lighting device for surface inspection according toclaim 1, comprising a switch that turns on/off supplied power of saidlight-emitting element main bodies.
 7. The lighting device for surfaceinspection according to claim 6, wherein said switch is operated inpulse modulation mode.
 8. A lighting device for surface inspectionaccording to claim 1, wherein reduction in the amount of loss of lightin the junction region is achieved by mounting LED on light guide inputterminal of optical fiber by means of a ball lens.